Cannula with sensors to measure patient bodywall forces

ABSTRACT

A cannula is provided that includes a head portion that defines a proximal opening sized to receive one or more surgical instruments; an elongated inner tube rigidly fastened to the head portion defines an elongated conduit; a surgical instrument can be inserted within the conduit; an elongated overtube rigidly fastened to the head portion is coaxially aligned with the inner tube and extends about a portion of the inner tube; an inner wall of the overtube is spaced apart from an outer wall of the inner tube; sensors are disposed on the overtube to provide an indication of forces applied to the outer wall of the overtube in a direction generally transverse to the longitudinal dimension of the overtube.

FIELD

The invention relates in general to minimally invasive surgical systems,and more particularly, to a cannulas used during minimum invasivesurgery.

BACKGROUND

Endoscopy may be the most common form of minimally invasive surgery.Perhaps the most common form of endoscopy is laparoscopy, which isminimally invasive inspection and surgery inside the abdominal cavity.In a typical laparoscopic surgery, a patient's abdomen is insufflatedwith gas, and cannula sleeves are passed through small (approximately ½inch) incisions to provide entry ports for laparoscopic surgicalinstruments.

As explained in U.S. Pat. No. 6,989,003, entitled, “Obturator andCannula for a Trocar Adapted for Ease of Insertion and Removal”, atrocar-cannula, commonly referred to as, a trocar, is a surgical deviceused to obtain access to a body cavity to perform various surgicalprocedures, such as, laparoscopic surgery or arthroscopic surgery.Typically, a trocar is an elongated, pointed surgical instrument thatincludes a pointed rod-like device, referred to in the art as an“obturator” that is fitted into a tube-like device that is referred toin the art as a “cannula”. The pointed, sometimes sharply pointed, endof the obturator projects out the end of the cannula and is used topenetrate the outer tissue of the cavity. After the tissue is penetratedand the body cavity, for example, is accessed by the trocar, theobturator is withdrawn from the cavity and the cannula is left in placein the cavity to provide a channel for accessing the cavity. The bodycavity can then be accessed by further surgical instruments via thecannula to perform various surgical procedures.

The laparoscopic surgical instruments generally include a laparoscopefor viewing the surgical field, and working tools defining endeffectors. Typical surgical end effectors include clamps, graspers,scissors, staplers, or needle holders, for example. The working toolsare similar to those used in conventional (open) surgery, except thatthe working end or end effector of each tool is separated from itshandle by, e.g., an approximately 12-inch long, extension tube.

To perform surgical procedures, the surgeon passes these working toolsor instruments through cannula sleeves to a required internal surgicalsite and manipulates them from outside the abdomen by sliding them inand out through the cannula sleeves, rotating them in the cannulasleeves, levering (i.e., pivoting) the instruments against the abdominalwall and actuating end effectors on the distal ends of the instrumentsfrom outside the abdomen. The instruments pivot around centers definedby the incisions which extend through muscles of the abdominal wall. Thesurgeon monitors the procedure by means of a television monitor whichdisplays an image of the surgical site via a laparoscopic camera. Alaparoscopic camera is also introduced through the abdominal wall andinto the surgical site. Similar endoscopic techniques are employed in,e.g., arthroscopy, retroperitoneoscopy, pelviscopy, nephroscopy,cystoscopy, cisternoscopy, sinoscopy, hysteroscopy, urethroscopy and thelike.

U.S. Pat. No. 7,155,315, entitled, “Camera Referenced Control in aMinimally Invasive Surgical Apparatus”, describes a minimally invasivetelesurgical system for use in surgery to increase a surgeon's dexterityas well as to allow a surgeon to operate on a patient from a remotelocation. Telesurgery is a general term for surgical systems where thesurgeon uses some form of remote control, e.g., a servomechanism, or thelike, to manipulate surgical instrument movements rather than directlyholding and moving the instruments by hand. In such a telesurgerysystem, the surgeon is provided with an image of the surgical site atthe remote location. While viewing typically a three-dimensional imageof the surgical site on a suitable viewer or display, the surgeonperforms the surgical procedures on the patient by manipulating mastercontrol devices, at the remote location, which control the motion ofservomechanically operated instruments.

The servomechanism used for telesurgery will often accept input from twomaster controllers (one for each of the surgeon's hands), and mayinclude two robotic arms. Operative communication between each mastercontrol and an associated arm and instrument assembly is achievedthrough a control system. The control system includes at least oneprocessor which relays input commands from a master controller to anassociated arm and instrument assembly and from the arm and instrumentassembly to the associated master controller in the case of, e.g., forcefeedback.

FIG. 1 is an illustrative drawing showing a known cannula 102 that actsas a conduit for receiving one or more instruments 104 extending througha patient's bodywall 106. The cannula includes a proximal end portion108 disposed outside the body cavity and a distal end portion 110 thatextends within the body cavity. An instrument 104 typically includes anelongated shaft portion 104-1 having an end effector portion 104-2coupled to a distal working-end thereof. In operation, longitudinal axesof the instrument 104 and the cannula 102 are aligned when theinstrument is inserted in the cannula. In some telesurgical systems, awrist-like mechanism 104-3 is located at the distal end of theinstrument between the shaft 104-1 and the end-effector 104-2 to allowrotational movement of the end effector within the body cavity.

Typically, during minimally invasive surgery, a surgeon manipulates theinstrument 104 to perform a surgical procedure from a distance, whichdiminishes the surgeon's ability to use physical touch as a source offeedback during surgery. The surgeon may manipulate an end effector104-2 disposed at the end of an elongated instrument shaft 104-1 thatextends through a cannula 102, for example. As a consequence, asurgeon's may lose the ability to sense the amount of force exerted uponinternal body tissue during the procedure. U. S. Patent Application Pub.No. 2011/0178477, entitled, Trocar Device for Passing a Surgical Tool,and N. Zemiti et al., A Force Controlled Laparoscopic Surgical Robotwithout Distal Force Sensing, Experimental Robotics IX, STAR 21, pages153-163, Springer-Verlag Berlin Heidelberg 2006, disclose trocar thatinclude sensors used to estimate the force exerted by an elongatedinstrument upon internal body tissue contacted by a surgical instrumentduring minimally invasive surgery.

SUMMARY

A cannula includes a head portion that defines a proximal opening sizedto receive one or more surgical instruments. An elongated inner tuberigidly fastened to the head portion defines an elongated conduitbetween the proximal opening and a distal opening. One or more surgicalinstruments can be inserted in through the proximal opening and extendthrough the conduit to the distal opening. An elongated overtube isrigidly fastened to the head portion and is coaxially aligned with theinner tube and extends about a portion of the inner tube. An inner wallof the overtube is apart from an outer wall of the inner tube. Sensorsare disposed on the overtube to provide an indication of forces appliedto the outer wall of the overtube in a direction generally transverse tothe longitudinal dimension of the overtube.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion. In addition, the present disclosuremay repeat reference numerals and/or letters in the various examples.This repetition is for the purpose of simplicity and clarity and doesnot in itself dictate a relationship between the various embodimentsand/or configurations discussed.

FIG. 1 is an illustrative side elevation cross-sectional view drawingshowing a known cannula that acts as a conduit for one or moreinstruments extending through a patient's bodywall.

FIG. 2 is an illustrative drawing representing certain forces exertedupon an instrument inserted within a cannula and resultant force upon apatient's bodywall.

FIG. 3A is an illustrative side elevation drawing of a first cannula inaccordance with some embodiments.

FIG. 3B is a cross-sectional view of the first cannula of FIG. 3A inaccordance with some embodiments.

FIG. 4 is an illustrative side elevation drawing of a second cannula inaccordance with some embodiments.

FIG. 5 is a perspective view of a six degree-of-freedom sensor inaccordance with some embodiments.

FIG. 6A is an illustrative cross-sectional drawing of the first cannulashowing an instrument disposed to collide with an inner tube inaccordance with some embodiments.

FIG. 6B is an illustrative cross-sectional drawing of the first cannulashowing an instrument disposed to impart a lever force to an inner tubein accordance with some embodiments.

FIGS. 6C1-6C4 are illustrative drawings showing longitudinalcross-sectional views of a portion of the overtube with four alternativesensor placement configurations in accordance with some embodiments.

FIG. 7 is an illustrative drawing representing an object that issubjected to axial force that changes its length dimension.

FIG. 8 is an illustrative drawings showing example of strain gaugesmounted on opposite sides of a longitudinal structure subjected to aforce transverse to a longitudinal axis of the structure.

FIG. 9 is an illustrative drawing of showing strain gauges arranged in arosette-like configuration in accordance with some embodiments.

FIG. 10 is an illustrative cross-sectional drawing of the second cannulain accordance with some embodiments.

DESCRIPTION OF EMBODIMENTS

The following description is presented to enable any person skilled inthe art to create and use a cannula with sensors isolated from forcesresulting from instrument-cannula collisions. Various modifications tothe embodiments will be readily apparent to those skilled in the art,and the generic principles defined herein may be applied to otherembodiments and applications without departing from the spirit and scopeof the inventive subject matter. Moreover, in the following description,numerous details are set forth for the purpose of explanation. However,one of ordinary skill in the art will realize that the inventive subjectmatter might be practiced without the use of these specific details.Identical reference numerals may be used to represent different views ofthe same item in different drawings. Thus, the inventive subject matteris not intended to be limited to the embodiments shown, but is to beaccorded the widest scope consistent with the principles and featuresdisclosed herein.

FIG. 2 is an illustrative drawing representing certain forces exertedupon an instrument inserted within a cannula and resultant force upon apatient's bodywall. Both during laparoscopic surgery and telesurgery,insertion and movement of the cannula and instruments inserted withinthe cannula results in forces exerted upon a patient's abdominalbodywall. The cannula and an instrument inserted within the cannula havelongitudinal axes, e.g., that extend generally parallel to a y-axis asshown. A surgeon, during laparoscopic surgery or telesurgery, may impartto a proximal end of the instrument that is disposed outside thepatient's body, a lateral force having a force component generallyperpendicular to the longitudinal axes of the cannula and theinstrument. The surgeon force upon the instrument is imparted to thecannula. In reaction, internal body tissue that is contacted by a distalend of the instrument, inside the body cavity, may exert to a distal endof the instrument that is disposed inside the patient's body, a lateralforce having a force component directed generally perpendicular to thelongitudinal axes of the cannula and the instrument. The internal bodytissue force upon the instrument is imparted to the cannula. Thebodywall, which is disposed between a site of the surgeon imparted forceand a site of the tissue imparted force, exerts a lateral directionreactive force, in response to a combination of the surgeon's force andthe tissue's force having a force component directed generallyperpendicular to the vertical axis of the cannula. More specifically,forces created in response to manipulation of instruments insertedwithin a cannula create a lever action in which a patient's bodywall isdisposed at or near the fulcrum. These forces associated with the leveraction exert stresses upon the bodywall tissue that can result in tissuetrauma.

FIG. 3A is an illustrative side elevation drawing of a first cannula 302in accordance with some embodiments. FIG. 3B is a cross-sectional viewof the first cannula 302 of FIG. 3A in accordance with some embodiments.The first cannula 302 includes a head portion 304 and an elongatedportion 306 that includes a coaxial elongated inner tube 308 andelongated overtube 310. The elongated portion 306, which includes theelongated inner tube 308 and elongated overtube 310 are generallycylindrical in contour. The elongated portion 306 depends from the headportion 304. More particularly, the inner tube 308 and the overtube 310are rigidly fastened (i.e. welded or otherwise mechanically connected)to the head portion 304. In some embodiments, the inner tube 308 and theovertube 310 are formed integrally with the head portion.

The inner tube 308 includes inner walls that define an elongated innerconduit sized to receive one or more surgical instruments 312 (only oneshown). The overtube 310 surrounds at least a portion of the inner tube308, and extends distally enough to come into contact with the bodywallsuch that all the loads from the bodywall are imparted on the overtubeand not the inner tube. The inner tube 308 is longer than the overtube310, and therefore, extends distally past the distal end of the overtube310. The inner tube 308 extending beyond the distal end of the overtubeensures that the instrument does not come into direct contact with theovertube during normal operation. The first cannula is shown with theelongated portion 306 extending through a patient's bodywall 314. Theinner tube 308 has a lateral dimension that is sized to receive one ormore surgical instruments and defines a distal opening at a distal endso as to provide surgical access within the patient's body. As morefully clearly represented in FIGS. 6A-6B, which are explained below, theovertube 310 is coaxially aligned with the inner tube 308 and islaterally spaced apart therefrom so as to not contact the inner tube 310during normal operation. More particularly, as shown more clearly inFIGS. 6A-6B, the inner tube outer diameter is sufficiently smaller thanthe overtube inner diameter so that the inner tube and the overtube donot come into contact during normal operation. Sensor devices 311disposed in contact with the overtube 310 wall are configured to providean indication of forces imparted to the overtube 310 by the bodywall314.

During a typical surgical procedure, the head portion 304 of the firstcannula 302 is disposed outside of the patient's body cavity, and atleast a portion of the elongated portion 306, which includes a portionof the inner tube 308 and a portion of the overtube 310, extends throughthe bodywall 314 to an interior of the patient's body cavity. Theelongated portion 306 has a longitudinal axis, e.g., generally parallelto a y-axis as shown. One or more surgical instruments can be insertedthrough the head portion 304 and extend generally parallel to the centeraxis through an instrument-receiving conduit defined by the inner tube308 so as to project out from the open distal end of the inner tube tothe interior of a patient's body.

In some embodiments, the head portion 304 and the inner tube 308comprise an integral structure that defines the instrument-receivingconduit in which the one or more instruments may be inserted. The headportion 304 defines a proximal opening 316 to the conduit. The proximalopening is enlarged so as to provide ease in insertion and removal ofinstruments, and conduit walls within the head portion are inclined soas to provide guide surfaces to guide instruments to the narrowerdiameter elongated portion of the conduit defined by the inner tube. Insome embodiments, the head portion 304 also includes a gas conduit (notshown) to introduce one or more gases through the inner tube forinsufflating the body cavity during a surgical procedure. In someembodiments, the head portion 304 also includes a seal (not shown) forpreventing gas from escaping the body cavity during insufflation in asurgical procedure. In some embodiments adapted for use duringlaparoscopic surgery, the head portion 304 is sized and shaped to beheld by a surgeon, for example, during insertion of a trocar (not shown)or withdrawal of an obturator (not shown), which form no part of thepresent invention.

The overtube 310 has stiffness such that it can deflect at one or morelocations along its longitudinal axis in response to forces impartedgenerally transverse to its longitudinal axis by a patient's bodywall314, e.g., including forces imparted generally in an x-axis or a z-axisdirection, during a typical surgical procedure. Moreover, the overtube310 stiffness and its lateral spacing from the inner tube 308 are suchthat an inner wall of the overtube and an outer wall of the inner tubedo not physically contact each other when the overtube deflects relativeto its longitudinal center axis in response to forces imparted to apatient's bodywall 314 during a typical surgical procedure. In someembodiments, spacing between the overtube and the inner tube comprises agap 307, which is represented more clearly in FIGS. 6A-6B as gap 607,which is narrow enough to not add significantly to overall diameter ofthe elongated portion 306 of the cannula 302 so as to not significantlyincrease the size of a surgical incision required to insert theelongated portion 306 into a patient's body.

During normal operation, the gap region 307 (described more fully belowand illustrated with reference to FIGS. 6A-6B) defined between the innertube and the overtube isolates the overtube 310 from deflections thatmay be imparted to the inner tube 308 due to instrument contact with theinner tube in the course of a surgical procedure, for example. Suchinstrument contact may involve an instrument banging against an innerwall of the inner tube due to a surgeon's or a teleoperated robot'smanipulation of instruments during a surgical procedure. The sensordevices (described more fully below) in contact with the overtube 310,therefore, are isolated from the effects of deflection forces imparteddue to collisions between the instrument and the inner tube 308. Thus, acannula in accordance with some embodiments can disambiguate forcesimparted by instrument collisions with an inner wall of the inner tubefrom bodywall loads imparted to the overtube.

FIG. 4 is an illustrative side elevation drawing of a second cannula 402in accordance with some embodiments. Features of the second cannula thatare substantially identical to those of the first cannula 302 areidentified by the same reference numerals used to identify thecorresponding features in FIGS. 3A-3B and are not further described. Thesecond cannula 402 includes a six degree-of-freedom (6-dof) sensordevice 403. In some embodiments, the 6-dof sensor 403 includes a Stewartplatform based force/torque sensor. The second cannula 402 includes ahead portion 404 and coaxially aligned elongated inner tube 408 andelongated overtube 410. The inner tube 408 is sized to receive one ormore surgical instruments 412 (only one shown). The overtube 410 of thesecond cannula 402 includes a first overtube portion 410-1 and a secondovertube portion 410-2, and the 6-dof sensor 403 is disposed between thefirst and second overtube portions.

FIG. 5 is a perspective view of a six degree-of-freedom sensor 403 inaccordance with some embodiments. The 6-dof force/sensor has an annularshape that defines a central opening 424 through which instruments (notshown) and the inner tube 408 can extend. In some embodiments, the 6-dofsensor includes silicon strain gages to sense forces. Referring again toFIG. 4, first overtube portion 410-1 rigidly depends from a head portion404 of the second cannula 402. The first overtube portion 410-1 includesa distal end that defines a first annular flange 428-1 sized tooperatively contact a proximal surface region 430 of the 6-dof sensor403. The second overtube portion 410-2 includes a proximal end thatdefines a second annular flange 428-2 sized to operatively contact adistal surface region 426 of the 6-dof sensor 403. Attachment fasteners(e.g., screws) 429 are visible also.

FIG. 6A is an illustrative cross-sectional drawing of the first cannula600 representing an example collision between an instrument 622 and theinner tube 604 in accordance with some embodiments. The first cannula600 includes the head portion 602 and the elongated portion 603. Thehead portion 602 defines an insufflation conduit 640 through which aninsufflating gas can be introduced inside the inner tube 604 and insidethe patient's body cavity via the inner tube during a surgicalprocedure. The elongated portion 603 includes the coaxial inner tube 604and overtube 606, which depends from the head portion 602. The innertube includes an inner wall 605 that defines the instrument-receivingconduit and an outer wall 619. The gap 607 is defined by an outer wall619 of the inner tube and an inner wall 616 of the overtube. Together,the head portion 602 and the inner wall 605 of the inner tube 604 definethe instrument-receiving conduit 608. The head portion 602 defines theproximal opening 610 to the conduit 608. A distal end of the inner tube604 defines a distal opening 612 to the conduit 608 adjacent to apatient's body cavity. Strain sensors 614 are disposed to contact aninner wall 616 of the overtube 604 and/or an outer wall 618 of theovertube 604 and are configured to measure strain imparted to theovertube.

Referring to the illustrative drawings of FIGS. 6C1-6C4, there are shownlongitudinal cross-sectional views of a portion of the overtube 606 withfour alternative sensor placement configurations in accordance with someembodiments. FIG. 6C1 shows an illustrative first sensor placement onouter wall 618 of the overtube 606. On one side of the outer wall 618,there is a sensor 614 and 180 degrees apart on the opposite outer wall618 from that sensor 614 there is the complementary sensor 614. FIG. 6C2shows an illustrative second sensor placement on inner wall 616 of theovertube 606. On one side of the inner wall 616, there is a sensor 614and on an opposed facing portion of the inner wall 616 there is thecomplementary sensor 614. FIG. 6C3 shows an illustrative third sensorplacement on both inner wall 616 and outer wall of the overtube 606. Onthe inner wall 616, there is a sensor 614 and on a portion of the outerwall 618 directly opposite that sensor 614 there is a complementarysensor 614. FIG. 6C4 shows an illustrative fourth sensor placement withredundant sensor placements like that of FIG. 6C3.

Referring again to FIG. 6A, during performance of a surgical procedure,the first cannula 600 extends through a patient's bodywall 620, and aninstrument 622 extends within the conduit 608 to reach inside thepatient's body cavity. The instrument 622 may include an end-effector624 for use in performing a surgical procedure. An operator 626, such asa surgeon or a teleoperation surgical system manipulates the instrument622 while it extends within the conduit 608 and into a patient's body.

During the procedure, a force F_(Operator) imposed by the operator 626upon the instrument 622 and/or a force F_(Tissue) imposed by patienttissue upon the instrument 622 may cause the instrument to collide withthe inner wall 605 of the inner tube 604,which imparts a forceF_(Instrument) upon the inner wall 605 of the inner tube 604. However,the instrument collision force is not imparted to the overtube 606 sinceit is isolated from the inner tube 604 by the gap 607. Thus the sensors614 configured to sense strain in the overtube 606 do not detectdeflections from force F_(Instrument) imparted due to collisions betweenthe instrument 622 and the inner tube 604.

It will be appreciated that the force F_(Instrument) upon the inner wall605 of the inner tube 604 imparts a load through the overtube 606 to thepatient's bodywall. However, the gap 607 between the inner tube 604 andthe overtube 606 isolates the overtube 606 from incurring deflectionsdue to collisions between the inner tube 604 and the instrument 622.Thus, deflections imparted to the overtube 606 result from patientbodywall forces, which may be responsive to a force F_(Instrument) uponthe inner wall 605 of the inner tube 604, but such deflections are notimparted due to the collisions between the instrument 622 and theovertube 606, since there are no such collisions.

The overtube 606 has a stiffness such that it can deflect relative toits longitudinal axis in response to lateral forces imparted by thepatient's bodywall 620, in a direction generally perpendicular to itslongitudinal axis, e.g. in an x-axis or z-axis direction, but having ancomponent force in the y-axis when the angle between the cannula andbodywall, e.g., ⊖, is not 90 degrees. Additionally the overtube 606 hasa compressive strength such that it can compress or stretch along it'slongitudinal axis in response to non-lateral bodywall forces, e.g. inthe y-axis direction.

More specifically, in some embodiments the overtube stiffness has apredictable and linear strain response to stress, i.e. a known young'smodulus. More specifically, in some embodiments, the stiffness of theovertube is great enough for the tube to deflect and not permanentlydeform under typical body wall loads of approximately 0-30 Newtons. Evenmore specifically, in some embodiments, the stiffness of the overtube isgreat enough for the tube to deflect and not permanently deform underloads of approximately 0-50 Newtons. In some embodiments, a stainlesssteel overtube with a wall thickness of approximately 0.005-0.050, witha preferred of approximately wall thickness range of approximately0.012-0.030, and an outside diameter of approximately 0.25-1 inches,with a preferred range of approximately 0.4-0.6 inches, has anacceptable stiffness to deflect but not permanently deform under normalloads from the bodywall. Preferably, in some embodiments, Spacingbetween the overtube and the inner tube should be great enough such thatthe inner diameter (ID) of the overtube does not touch the outerdiameter (OD) of the inner tube when the overtube deflects, but smallenough such that the outer diameter of the overtube represents typicalcannula diameters in minimally invasive surgery. In some embodiments,the spacing, 607 of FIG. 6A, between the overtube ID and inner tube ODis approximately 0.007-0.1 inches, with a preferred range ofapproximately 0.015-0.035 inches.

FIG. 6B is an illustrative cross-sectional drawing of the first cannula600 showing an instrument 622 disposed to impart a lever force to theinner tube 604 in accordance with some embodiments. It will beappreciated that FIG. 6A and FIG. 6B are identical except for thedisposition of the instrument within the inner tube and the forcesimparted. Assume that an operator imparts a force F_(Operator) and thetissue imparts a force F_(Tissue) that cause the instrument 622 to pushto the left in FIG. 6B against an inner wall 605 of the inner tube 604adjacent a proximal end of the inner tube 604 and that cause theinstrument 622 to push to the right in FIG. 6B against the inner wall605 of the inner tube 604 adjacent a distal end of the inner tube 604.Under these conditions, for example, the first cannula 600 acts as alever having a fulcrum at a location generally indicated by dashed lines630, at about the location of the bodywall 620.

Under these conditions, a bodywall force F_(Bodywall) is imparted to thepatient's bodywall 620. The bodywall force can be a torque or a force,for example, in which a distal end of the overtube 606 imparts a forcein a direction generally to the right in the drawing and a proximal endof the overtube 606 imparts a force in a direction generally to the leftin the drawing, for example. The torque force to the overtube 606 aboutan x-axis and/or the z-axis, for example, centered at about the locationof the bodywall 620. In accordance with some embodiments, the bodywallforce F_(Bodywall) is imparted to the overtube 606, which may deflect inresponse to the bodywall force. The sensors 614 can detect strain in theovertube that results from the force or torque and can provide a measureof the strain.

The sensor devices 614 are disposed in physical contact with theovertube 606 to measure deflection of the overtube 606. Sensor devicescan be disposed in contact with an external wall 618 of the overtube, incontact with an interior wall 616 of the overtube or in contact withboth. In some embodiments, the sensor devices 614 are configured to actas strain gauges. Strain is a measure of the amount of deformation of abody due to an applied force. More specifically, strain can be definedas the fractional change of length.

FIG. 7 is an illustrative drawing representing an object 702 that issubjected to axial force that changes its length dimension. The lengthof the object in the absence of the forces is L. The change in theobject's length in response to the forces is ΔL.

Strain can be defined as: ε=ΔL/L.

FIG. 8 is an illustrative drawings showing example of first and secondstrain gauges 802-1, 802-2 mounted on opposite sides of a longitudinalstructure 804 that depends horizontally from a fixture 806 and that issubjected to a force transverse to a longitudinal axis (L) of thestructure 804. An example generally downward uniaxial force impartedtransverse to a longitudinal axis of the structure places the firststrain gauge 802-1 having an at rest length L₁ mounted on a side of thestructure to which the force is imposed in tension, resulting in anincrease in the length dimension of the first strain gauge 802-1 toL₁+ΔL₁. Conversely, the downward uniaxial force imparted transverse tothe longitudinal axis of the structure 804 places the second straingauge 802-2 having an at rest length L₁ mounted on a side of thestructure 804 opposite to that to which the force is imposed incompression, resulting in a decrease in the length dimension of thesecond strain gauge 802-2 to L1−ΔL₂. In accordance with someembodiments, strain gauges are mounted to the inner wall 616 and theouter wall 618 of the overtube 606 and may be spaced around the overtubein a variety of configurations in order to measure the applied forces inmultiple directions.

As explained above with reference to FIG. 6B, moments from the bodywallcan create complex tube deflection that includes tension and compressionsimultaneously along various points in length of the loaded member. Insome embodiments, such moments can be calculated when a staggeredconfiguration of strain gauges is used because the strain gauges areexperiencing both tension and compression at known points along innerand outer walls of the surface of the overtube.

FIG. 9 is an illustrative drawing of showing strain gauges 902 arrangedin a rosette-like configuration in accordance with some embodiments.Strain gauges are well known to persons of ordinary skill in the art. Insome embodiments, a strain gauge may comprise a grid pattern 904 thatincludes a very fine metallic wire, foil, fiber, etc. arranged in a gridpattern. The grid 904 is bonded to a thin backing (not shown), commonlyreferred to as a carrier which is directly attached to an item for whichstrain is to be measured. Strain that is experienced by such item istransferred directly to the strain gauge, which responds with a known,e.g., linear, change in electrical resistance. In a rosette-likeconfiguration, multiple strain gauges are positioned at known angles(e.g., α, β, γ) to one another in a rosette-like layout to convertlongitudinal strain into three independent components of plane strain.In accordance with some embodiments, groupings of sensors arranged in arosette structure can be staggered along the inner wall 616 and outerwall 618 of the overtube 606 to measure moments about the x-axis andz-axis.

FIG. 10 is an illustrative cross-sectional drawing of the second cannula1000 in accordance with some embodiments. The second cannula 1000includes an annular 6-dof sensor 632. The overtube 606 includes thefirst overtube portion 636 that includes the first annular flange 638sized to operatively contact a proximal surface region 640 of the 6-dofsensor 632. The overtube 606 includes the second overtube portion 642that has a proximal end that defines the second annular flange 644 sizedto operatively contact a distal surface region 646 of the 6-dof sensor632. Thus, the second overtube portion 642 is suspended from the 6-dofsensor 632. It will be appreciated that in other respects the first andsecond cannulas of FIG. 6A-6B and FIG. 10 are substantially the same.

The foregoing description and drawings of embodiments in accordance withthe present invention are merely illustrative of the principles of theinvention. Therefore, it will be understood that various modificationscan be made to the embodiments by those skilled in the art withoutdeparting from the spirit and scope of the invention, which is definedin the appended claims.

1. A cannula comprising: a head portion that defines a proximal openingsized to receive one or more surgical instruments; an inner tube, havingan elongated longitudinal dimension, that depends from and is rigidlyfastened to the head portion and that defines a distal opening, whereinthe inner tube includes an inner wall that defines an elongated conduitbetween the proximal opening and the distal opening, wherein the innerwall has a transverse dimension sized to receive the one or moreinstruments inserted in through the proximal opening and extendingthrough the conduit to the distal opening, and wherein the inner tubeincludes an outer wall; an overtube, having an elongated longitudinaldimension, that is coaxially aligned with the inner tube and thatextends about a portion of the inner tube and that depends from and isrigidly fastened to the head portion and that includes an inner wallthat is spaced apart from the outer wall of the inner tube, wherein theovertube includes an outer wall; and one or more sensors disposed toprovide an indication of at least one of a force and a moment applied tothe outer wall of the overtube in a direction generally transverse tothe longitudinal dimension of the overtube.
 2. The cannula of claim 1,wherein the one or more sensors are disposed to provide an indication ofdeflection of at least one of the inner wall and the outer wall of theovertube in a direction generally transverse to the longitudinaldimension of the overtube.
 3. The cannula of claim 1, wherein the one ormore sensors are disposed to provide an indication of deflection of theinner wall and the outer wall of the overtube in a direction generallytransverse to the longitudinal dimension of the overtube.
 4. The cannulaof claim 1, wherein the one or more sensors are disposed to provide anindication of at least one of a force and a moment imparted to theovertube about an axis generally transverse to the longitudinaldimension of the overtube.
 5. The cannula of claim 1, wherein the one ormore sensors include at least one sensor disposed on the inner wall ofthe overtube and at least one sensor disposed on the outer wall of theovertube.
 6. The cannula of claim 1, wherein the one or more sensorsinclude one or more strain gauges.
 7. The cannula of claim 1, whereinthe one or more sensors include multiple sensors attached at multiplelocations on one or both of the inner wall and the outer wall of theovertube.
 8. The cannula of claim 1, wherein the one or more sensorsincludes multiple sensors disposed in a rosette-like pattern.
 9. Thecannula of claim 1, wherein the overtube has a stiffness to deflect butnot permanently deform under normal human bodywall loads duringminimally invasive surgery.
 10. The cannula of claim 1, wherein theovertube has a stiffness to deflect but not permanently deform underloads of approximately 0-50 Newtons.
 11. The cannula of claim 1, whereinthe overtube has a stiffness to deflect but not permanently deform undernormal human bodywall loads during minimally invasive surgery; andwherein a gap between the outer wall of the inner tube and the innerwall of the outer tube is large enough that the outer wall of the innertube does not contact the inner wall of the overtube under normalbodywall loads during minimally invasive surgery.
 12. The cannula ofclaim 1, wherein the overtube has a stiffness to deflect but notpermanently deform under loads of approximately 0-50 Newtons; andwherein a gap between the outer wall of the inner tube and the innerwall of the outer tube is large enough that the outer wall of the innertube does not contact the inner wall of the overtube under loads ofapproximately 0-50 Newtons.
 13. The cannula of claim 1, wherein theouter wall of the overtube has a transverse dimension that is suitablefor minimally invasive surgery.
 14. The cannula of claim 1, wherein theouter wall of the overtube has a transverse dimension that isapproximately 0.25-1 inches.
 15. The cannula of claim 1, wherein theovertube has a stiffness to deflect but not permanently deform undernormal human bodywall loads during minimally invasive surgery; wherein agap between the outer wall of the inner tube and the inner wall of theouter tube is large enough that the outer wall of the inner tube doesnot contact the inner wall of the overtube under normal bodywall loadsduring minimally invasive surgery; and wherein the outer wall of theovertube has a transverse dimension that is suitable for minimallyinvasive surgery.
 16. The cannula of claim 1, wherein the overtube has astiffness to deflect but not permanently deform under loads ofapproximately 0-50 Newtons; and wherein a gap between the outer wall ofthe inner tube and the inner wall of the outer tube is large enough thatthe outer wall of the inner tube does not contact the inner wall of theovertube under loads of approximately 0-50 Newtons; and wherein theouter wall of the overtube has an outer diameter of approximately 0.25-1inches.
 17. The cannula of claim 1, wherein the overtube comprisesstainless steel having a thickness of approximately 0.012-0.030 inchesand an outer diameter of approximately 0.25-1 inches inches.
 18. Thecannula of claim 1, wherein the inner tube has a greater longitudinaldimension than the overtube.
 19. The cannula of claim 1, wherein theinner tube has and the overtube are substantially cylindrical in contour20. A cannula comprising: a head portion that defines a proximal openingsized to receive one or more surgical instruments; an inner tube, havingan elongated longitudinal dimension, that depends from and is rigidlyfastened to the head portion and that defines a distal opening, whereinthe inner tube includes an inner wall that defines an elongated conduitbetween the proximal opening and the distal opening, wherein the innerwall has a transverse dimension sized to receive the one or moreinstruments inserted in through the proximal opening and extendingthrough the conduit to the distal opening, and wherein the inner tubeincludes an outer wall; an overtube having a first portion and a secondportion that are coaxially aligned with the inner tube; one or moresensors interposed between the first portion of the overtube and thesecond portion of the overtube wherein the first portion of the of theovertube depends from and is rigidly fastened to the head portion andincludes a first inner wall portion that is spaced apart from the outerwall of the inner tube, wherein the first portion of the overtubeincludes a first outer wall portion; wherein the second portion of theovertube has an elongated longitudinal dimension and includes a secondinner wall portion that is spaced apart from the outer wall of the innertube, wherein the second portion of the overtube includes a second outerwall portion wherein the one or more sensors are disposed to provide anindication of a force applied to the second outer wall portion in adirection generally transverse to the longitudinal dimension of theovertube.